Why decibels are logarithmic
Audio levels span a very large range, so decibels express ratios on a compact logarithmic scale. A decibel value is not a physical level until it has a reference such as dBFS, dBu, dBV, or SPL.
Amplitude versus power
Use 20 times the base-10 logarithm for like-for-like amplitude quantities such as voltage or sound pressure, and 10 times the logarithm for power quantities. The calculator displays both so their different numerical relationships are clear.
Reading common changes
About +6.02 dB doubles amplitude, while +3.01 dB doubles power. A -6 dB fader move produces roughly half the amplitude, not silence. Perceived loudness also depends on frequency, duration, listening level, and programme material.
Gain staging
Use adequate headroom through recording, mixing, and playback chains. A ratio calculation cannot identify clipping, noise, intersample peaks, calibration errors, or the acoustic level reaching a listener.
How the calculation works
Amplitude ratio = 10^(dB/20); power ratio = 10^(dB/10); amplitude dB = 20 log10(ratio).
